diff options
Diffstat (limited to 'bip-0347.mediawiki')
| -rw-r--r-- | bip-0347.mediawiki | 6 |
1 files changed, 3 insertions, 3 deletions
diff --git a/bip-0347.mediawiki b/bip-0347.mediawiki index 981af81..0aed70d 100644 --- a/bip-0347.mediawiki +++ b/bip-0347.mediawiki @@ -42,9 +42,9 @@ OP_CAT aims to expand the toolbox of the tapscript developer with a simple, modu * Post-Quantum Lamport signatures in Bitcoin transactions. Lamport signatures merely require the ability to hash and concatenate values on the stack. <ref>J. Rubin, "[bitcoin-dev] OP_CAT Makes Bitcoin Quantum Secure [was CheckSigFromStack for Arithmetic Values]", 2021, https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2021-July/019233.html</ref> It has been proposed that if ECDSA is broken or a powerful computer was on the horizon, there might be an effort to protect ownership of bitcoins by allowing people to mark their taproot outputs as "script-path only" and then move their coins into such outputs with a leaf in the script tree requiring a Lamport signature. It is an open question if a tapscript commitment would preserve the quantum resistance of Lamport signatures. Beyond this question, the use of Lamport Signatures in taproot outputs is unlikely to be quantum resistant even if the script spend-path is made quantum resistant. This is because taproot outputs can also be spent with a key. An attacker with a sufficiently powerful quantum computer could bypass the taproot script spend-path by finding the discrete log of the taproot output and thus spending the output using the key spend-path. The use of "Nothing Up My Sleeve" (NUMS) points as described in [[bip-0341.mediawiki|BIP341]] to disable the key spend-path does not disable the key spend-path against a quantum attacker as NUMS relies on the hardness of finding discrete logs. We are not aware of any mechanism which could disable the key spend-path in a taproot output without a softfork change to taproot. * Non-equivocation contracts <ref>T. Ruffing, A. Kate, D. Schröder, "Liar, Liar, Coins on Fire: Penalizing Equivocation by Loss of Bitcoins", 2015, https://web.archive.org/web/20221023121048/https://publications.cispa.saarland/565/1/penalizing.pdf</ref> in tapscript provide a mechanism to punish equivocation/double spending in Bitcoin payment channels. OP_CAT enables this by enforcing rules on the spending transaction's nonce. The capability is a useful building block for payment channels and other Bitcoin protocols. * Vaults <ref>M. Moser, I. Eyal, and E. G. Sirer, Bitcoin Covenants, http://fc16.ifca.ai/bitcoin/papers/MES16.pdf</ref> which are a specialized covenant that allows a user to block a malicious party who has compromised the user's secret key from stealing the funds in that output. As shown in <ref>A. Poelstra, "CAT and Schnorr Tricks II", 2021, https://www.wpsoftware.net/andrew/blog/cat-and-schnorr-tricks-ii.html</ref> OP_CAT is sufficient to build vaults in Bitcoin. -* Replicating CheckSigFromStack <ref>A. Poelstra, "CAT and Schnorr Tricks I", 2021, https://medium.com/blockstream/cat-and-schnorr-tricks-i-faf1b59bd298</ref> which would allow the creation of simple covenants and other advanced contracts without having to presign spending transactions, possibly reducing complexity and the amount of data that needs to be stored. Originally shown to work with Schnorr signatures, this result has been extended to ECDSA signatures <ref>R. Linus, "Covenants with CAT and ECDSA", 2023, https://gist.github.com/RobinLinus/9a69f5552be94d13170ec79bf34d5e85#file-covenants_cat_ecdsa-md</ref>. +* Replicating CheckSigFromStack <ref>A. Poelstra, "CAT and Schnorr Tricks I", 2021, https://www.wpsoftware.net/andrew/blog/cat-and-schnorr-tricks-i.html</ref> which would allow the creation of simple covenants and other advanced contracts without having to presign spending transactions, possibly reducing complexity and the amount of data that needs to be stored. Originally shown to work with Schnorr signatures, this result has been extended to ECDSA signatures <ref>R. Linus, "Covenants with CAT and ECDSA", 2023, https://gist.github.com/RobinLinus/9a69f5552be94d13170ec79bf34d5e85#file-covenants_cat_ecdsa-md</ref>. -OP_CAT was available in early versions of Bitcoin. +OP_CAT was available in early versions of Bitcoin. In 2010, a single commit disabled OP_CAT, along with another 15 opcodes. Folklore states that OP_CAT was removed in this commit because it enabled the construction of a script whose evaluation could have memory usage exponential in the size of the script. For example, a script that pushed a 1-byte value on the stack and then repeated the opcodes OP_DUP, OP_CAT 40 times would result in a stack element whose size was greater than 1 terabyte assuming no maximum stack element size. As Bitcoin at that time had a maximum stack element size of 5000 bytes, the effect of this expansion was limited to 5000 bytes. @@ -109,5 +109,5 @@ An alternative implementation of OP_CAT can be found in Elements <ref>Roose S., ==Acknowledgements== -We wish to acknowledge Dan Gould for encouraging and helping review this effort. We also want to thank Madars Virza, Jeremy Rubin, Andrew Poelstra, Bob Summerwill, +We wish to acknowledge Dan Gould for encouraging and helping review this effort. We also want to thank Madars Virza, Jeremy Rubin, Andrew Poelstra, Bob Summerwill, Tim Ruffing and Johan T. Halseth for their feedback, review and helpful comments. |